在通常情况下,序数词前要用定冠词。如: May is the fifth month. 5月是一年的第5个月。 That was the third time he had entered the house. 那是他第3次进入这座房子。 In came the first runner, closely followed by the second. 第一位赛跑者进来了,紧跟着第二位也进来了。 但是,如果序数词前使用了物主代词或所有格之类的修饰语,则不能使用定冠